Electrical switch utilizing compressed gas for arc extinction

ABSTRACT

An electrical switch structure utilizing a compressed gas such as SF6 for arc extinction comprises a high-pressure section, a low-pressure section and a switching point controlled by a blast valve located intermediate the high- and low-pressure sections. The gas flows in a closed circuit from the high-pressure section through the switch contacts to the low-pressure section, thence to a compressor which recompresses the gas and thence back to the high-pressure section. Included in the gas circuit between the compressor outlet and the high-pressure section is a buffer vessel which operates at a pressure higher than that of the highpressure section, and the necessary pressure reduction is attained by means of an interposed reducing valve. Another reducing valve is located in a line extending from the buffer vessel to the low-pressure section. Operation of the compressor is controlled solely as a function of the pressure level in the low-pressure section.

I Umted States Patent 1151 3,637,965 Schm1tz 1451 Jan. 25, 1972 [54] ELECTRICAL SWITCH UTILIZING FOREIGN PATENTS OR APPLICATIONS COMPRESSED GAS FOR ARC 696,066 10/1964 Canada ..200/14s E EXTINCTION Primary Examiner- Robert S. Macon [72] Inventor. Wolfgang Schmrtz, Brrkenau, Germany Anomey pierce Schemer & Parker [73] Assignee: Aktiengesellschaft Brown, Boveri & Cie,

Baden, Switzerland B RACT [22] Filed; M 19, 1970 An electrical switch structure utilizing a compressed gas such as SP for arc extinction comprises a high-pressure section, a [Zl] Appl. No.: 21,021 low-pressure section and a switching point controlled by a blast valve located intermediate the highand low-pressure 3 Foreign Appficafion Priority Data sections. The gas flows in a closed circuit from the high-pressure section through the switch contacts to the low-pressure P 1969 m ny l 1 7 section, thence to a compressor which'recompresses the gas and thence back to the high-pressure section. Included in the [52] US. Cl ..200/l48 E gas circuit between the compressor outlet and the high-pres [51] Int. Cl. ..H0lh 33/80 r ti is a buffer vessel which operates at a pressure Field of Search 143 4 143 B higher than that .of the high-pressure section, and the necessary pressure reduction is attained by means of an interposed References Cited reducing valve. Another reducing valve is located in a line extending from the buffer vessel to the low-pressure section. UNITED STATES PATENTS Operation of the compressor is controlled solely as a function 3,009,042 1 1/1961 Schrameck et al ..200 14s B of the Pressure level in the low-Pressure Section I 5 Claims, 2 Drawing Figures BUFFER VESSEL REL PATENTED m5 1912 SHEET 2 BF 2 INVENTOk. Wolfgang Schrnut 2 Ai orneas ELECTRICAL SWITCH UTILIZING COMPRESSED GAS FOR ARC EXTINCTION The present invention relates to a compressed gas switch or a compressed gas-insulated switching plant with a highand a low-pressure section and closed gas cycle, where the high pressure section is connected with the low-pressure section over at least one switching point provided with a blast valve and/or over a safety valve which responds at a maximum permissible pressure in the high pressure section, and where the gas return from the low-pressure section to the high pressure section occurs by means of one or more compressors.

In such switches and switch plants, there are located between the high-pressure section and the low-pressure section the switching points to which during switching the blowing jet is applied due to pressure difference between the two sections. The lower pressure section, which intercepts the outflowing switching gases, serves at the same time to insulate the electric installation parts. In such switches and switch plants it is important, therefore, that both the pressure difierence 1 between high-pressure and low-pressure sections required for. switching as well as the pressure level or gas density in the lowpressure section required for maintenance of the insulation be provided.

Since such compressed gas switches and switch plants are usually exposed to considerable temperature variations, the pressure level of the gas varies according to the temperature, or, if the pressure level is maintained constant, the density of the gas varies, and this would have to be taken into account in rating the insulation.

To take these relationships into consideration, various pressure or density controls have already been proposed, which, however, are quite expensive. For example, the temperaturecompensated pressure switch described in German patent 1,166,878, by means of which the compressor is to be actuated, can unfortunately be produced only at considerable expense. In order that the correct correlation of pressure and temperature will be insured automatically, a careful adjustment must be made, which is laborious.

For this reason it has been proposed in German patent 1,226,684 to avoid the known temperature-compensated control switches by using several temperature-independent pressure monitors, one of which is rendered operative through a thermostat, depending on the temperature. This, however, results in a multiplication of the number of pressure monitors, so that cost and trouble proneness cannot be reduced to the desired extent.

Another proposal, as disclosed in German patent 1,261,220, relates to the control of a compressed gas switch with a closed gas circuit and provides that the pressure-dependent locking members required for the switch can be actuated by a temperature-independent pressure monitor for each in the highand low-pressure sections of the gas circuit, the two pressure monitors being so adjusted in their working ranges that one picks up the critical values at high temperatures, the other at low temperatures. This arrangement, however, is made to fit the special case referred to. Besides, just as in the previously mentioned proposal, it results in unsteadiness in the operating characteristics, which may be undesirable.

The problem underlying the invention is that of making available in electric switch plants and compressed gas switches of the above-named kind, with simplest means, the high pressure required for extinguishing the arc and for driving the switch or respectively the required pressure difference as well as the low pressure needed for insulating, rated according to the required minimum gas density, and so controlling them solely as a function of the pressure levels that the pressures do not drop below the required minimum and the permissible maximum values are not exceeded.

This problem is solved according to the invention in that in the switches of the above-mentioned kind there is located in the closed gas circuit a buffer vessel of a pressure higher than in the high-pressure section, to which are connected both the high-pressure section and the low-pressure section through corresponding reducing valves, and that the compressor, connected to the low-pressure scction,'and controlled solely by the pressure level in the low-pressure section, is connected by its outlet to the buffer vessel.

For further elucidation of the invention and its method of operation, reference will now be made to the accompanying drawing:

FIG. 1 shows in schematic arrangement the gas circulation of the switch or switch plant according to the invention, and

FIG. 2, a diagram in which are represented the pressuretemperature state variations of sulfur hexafluoride (SP at constant volume, with the preferred operating characteristics of the switch or switch plant according to the invention.

As is evident from FIG. 1, the compressed gas switch or respectively the switch plant S has a high-pressure section HI) and a low-pressure section ND. Between them is arranged a switching point with respective blast valve V,,, which during switching operations permits the gas of the high-pressure section to flow via the switching point to the low-pressure section. The low-pressure section as well as the high-pressure, section are connected via their own reducing valves V,, V, to a buffer vessel P of a pressure higher than the-high-pressure section. The high-pressure section is then further connected via a safety valve V with the low-pressure section. Thereby the maximum occurring pressure is limited and the dimensions of the high-pressure section can be reduced accordingly. Via an additional valve V,, and a filter Fi the low-pressure section is connected to a compressor K, which via another filter Fi feeds into the buffer vessel P, whereby the gas circuit is closed. As additional safety measures there are provided: a safety valve V connected to the low-pressure section, a safety valve V connected to the buffer vessel P, and a spare gas vessel F, connected to the bufier vessel via another reducing -valve V,. In addition, the low and high pressure sections are each provided with a common pressure monitor W, and W respectively.

The invention proceeds fromthe necessity of providing in the low-pressure section a certain minimum gas density p,,,,,, (cf. FIG. 2) to maintain the insulation. For the highest temperature t to be taken into consideration, a certain minimum pressure P,,,,,, is correlated to this minimum gas density. It follows from this that in the low-pressure section a lower operating pressure P, must always exist, which is above the minimum pressure P,,,,,,. This lower operating pressure P is always available from the buffer vessel P via the reducing valve V,.

As a result of switching operation, temperature rises, or also as a result of overflow of the high-pressure section HD, a raise of pressure occurs in the low-pressure section ND. This is permissible up to an upper operating pressure P, fixed at will. When this upper operating pressure is reached in the low-pressure section, compressor K responds, draws off gas from the low-pressure section, and pumps it into the buffer vessel P. This goes on until a normal pressure P has adjusted itself in the low-pressure section which preferably, but not necessarily, corresponds at the highest operating temperature 1,, to a normal gas density p,,. As normal gas density p,, there is to be regarded the gas density which prevails at the lower operating temperature 1,, and lower operating pressure P,. Upon reaching the normal pressure P the compressor shuts off again.

For operational switching, that is, for applying a blast jet on the switching (contact interrupting) point between the highand low-pressure sections, a sufficient pressure difference, determined by a minimum pressure level P, in the high-pressure section, is required. This minimum pressure level P, depends, of course, on the greatest possible upper operating pressure P, in the low-pressure section, that is, it must be high enough in relation to P and is held in continuous readiness by the reducing valve V,, through which the high-pressure section is connected to the buffer vessel. For this purpose the buffer vessel is adjusted to a pressure level P which must be sufficiently above a highest permissible pressure value P, of the high-pressure section,

Due to a temperature change, e.g., from 1,, to t the pressure in the high-pressure section might increase to impermissible values, exceeding the maximum permissible pressure value P To prevent this is the function of safety valve V which responds when the maximum permissible pressure value P is reached and which lets gas flow into the low-pressure section. if this then leads to too great a pressure increase in the lowpressure section (the upper operating pressure P is being exceeded), the compressor goes into operation in the manner described above.

The additional safety measures work as follows:

The safety valve V connected to the low-pressure section is adjusted to a pressure P. above the upper operating pressure P and sees to it that in case of disturbance e.g., failure of the compressor) the pressure in the low-pressure section cannot rise too high. The magnet value V,, closes the line leading from the low-pressure section to the compressor when in case of disturbance (compressor running through) the minimum pressure P is reached, thus seeing to it that the compressor cannot draw too much gas from the low-pressure section. The safety valve V connected to the buffer vessel P responds at a maximum pressure limit P permissible for the buffer vessel and, if necessary, lets the compressed gas escape into the open. Lastly, an additional gas supply F, connected via a reducing valve V to the buffer vessel P and which is adjusted to the nominal pressure P, of the buffer vessel, sees to it that any gas losses in the switch or respectively in the switch plant can be compensated.

The advantages achieved with the invention thus consist chiefly in that, by simple means, the pressure levels required for extinguishing the are at the switching point and for driving the switch, or respectively the necessary pressure differences, as well as the low pressure needed for insulating, are made available, the pressure levels especially in the low-pressure section being arranged so that the minimum gas density required for sufficient insulation is provided, and this without having to resort to temperature compensation devices or gas density measurements for the control of the gas circulation. It is quite sufficient in the invention to control the compressor by way of a simple control scheme by means of the pressure monitor W simply as a function of the two pressure levels P and P of the low-pressure section. The alternation between inflow and outflow of gas caused by the change in temperature has the further advantage that the gas can be guided over filters independently of switching operations and can thus be purified and dehumidified. Thereby a positive flushing of the insulators arranged in the low-pressure section is achieved, which is of great advantage for the life of the installation. The automatic gas circulation, independent of switching operations, can be extended by placing the pressure level (normal pressure P responsible for the shutting off of the compressor below the response pressure (lower operating pressure P )of the reducing valve V Then, of course, a time relay, for example, is needed to turn off the compressor, By this measure, however, an extended positive flushing of the insulation parts in the low-pressure section under voltage stress is obtained.

Iclaim:

1. In an electrical switch structure utilizing compressed gas for are extinction, the combination comprising a high-pressure section, a low-pressure section, a switching point controlled by a blast valve intermediate said highand low-pressure sections whereby upon operation of said blast valve the gas passes from said high-pressure section through said switching point to said low-pressure section, a closed gas circuit extending from said low-pressure section to said high-pressure section for gas flow between said sections, said gas circuit including in series a compressor and a buffer vessel having a pressure higher than that which exists in said high-pressure section and which is obtained by means of a first reducing valve located in said circuit between said buffer vessel and said high-pressure section, the inlet to said compressor being connected to said low-pressure section, the outlet from said compressor being connected to said buffer vessel and said compressor being controlled solely by the level of the pressure m said low-pressure section, an auxiliary gas flow line extending directly from said buffer vessel to said low-pressure section, and a second reducing valve located in said auxiliary gas flow line for maintaining a minimum pressure in said low pressure section.

2. An electrical switch structure as defined in claim I and which further includes first and second safety valves connected respectively to said low-pressure section and buffer vessel and which lead to the surrounding atmosphere, and an additional supply of pressurized gas connected to said buffer vessel through a reducing valve adjusted to the nominal pressure assigned to said buffer vessel.

3. An electrical switch structure as defined in claim 1 and which further includes a pressure-controlled valve located in said gas circuit between said low-pressure section and the inlet to said compressor, said valve being normally open and movable to a closed position in response to a minimum pressure level below the normal operating pressure in said low-pressure section.

4. An electrical switch structure as defined in claim 1 and which further includes a time relay which is conditioned upon reaching a lower operating pressure to turn off said compressor which starts up at the upper operating pressure.

5. An electrical switch structure as defined in claim 1 wherein a plurality of individual compressed gas switches are connected in parallel to a common buffer vessel. 

1. In an electrical switch structure utilizing compressed gas for arc extinction, the combination comprising a high-pressure section, a low-pressure section, a switching point controlled by a blast valve intermediate said high- and low-pressure sections whereby upon operation of said blast valve the gas passes from said high-pressure section through said switching point to said low-pressure section, a closed gas circuit extending from said low-pressure section to said high-pressure section for gas flow between said sections, said gas circuit including in series a compressor and a buffer vessel having a pressure higher than that which exists in said high-pressure section and which is obtained by means of a first reducing valve located in said circuit between said buffer vessel and said high-pressure section, the inlet to said compressor being connected to said low-pressure section, the outlet from said compressor being connected to said buffer vessel and said compressor being controlled solely by the level of the pressure in said low-pressure section, an auxiliary gas flow line extending directly from said buffer vessel to said low-pressure section, and a second reducing valve located in said auxiliary gas flow line for maintaining a minimum pressure in said low pressure section.
 2. An electrical switch structure as defined in claim 1 and which further includes first and second safety valves connected respectively to said low-pressure section and buffer vessel and which lead to the surrounding atmosphere, and an additional supply of pressurized gas connected to said buffer vessel through a reducing valve adjusted to the nominal pressure assigned to said buffer vessel.
 3. An electrical switch structure as defined in claim 1 and which further includes a pressure-controlled valve located in said gas circuit between said low-pressure section and the inlet to said compressor, said valve being normally open and movable to a closed position in response to a minimum pressure level below the normal operating pressure in said low-pressure section.
 4. An electrical switch structure as defined in claim 1 and which further includes a time relay which is conditioned upon reaching a lower operating pressure to turn off said compressor which starts up at the upper operating pressuRe.
 5. An electrical switch structure as defined in claim 1 wherein a plurality of individual compressed gas switches are connected in parallel to a common buffer vessel. 